Most types of fluid valves include a moveable stem or poppet that is used to move a fluid closure element. Such valves require one 10 or more sealing elements to prevent fluid from leaking around the moveable stem.
FIG. 1 shows a typical pneumatic valve 10 of a type known in the prior art. Valve 10 has a body 12. The body houses an inlet chamber 16, as well as an outlet chamber 14 and an exhaust chamber 18. The inlet chamber 16 is connected to a supply of compressed air. The outlet chamber is connected to a fluid power device such as a pneumatic cylinder. The exhaust chamber is open to atmosphere.
A stem 20 extends through the inlet and outlet chambers. Stem 20 is moveable in the vertical direction as the valve is shown in FIG. 1. The stem includes an upper portion 22 which is in operative connection with means for moving the stem. In a typical application, an electrical solenoid is used for this purpose. The stem is biased upward in the body as shown in FIG. 1 by a spring 24 which contacts a lower portion 26 of the stem.
The stem has thereon a first enlargement 28 and second enlargement 30. The enlargements are comprised of resilient material. First enlargement 28 is positioned adjacent to a first seat 32. Second enlargement 30 is positioned adjacent a second seat 34. In a first position of the stem 20 shown in FIG. 1, first enlargement 28 abuts first seat 32. As a result, compressed air delivered to the inlet chamber 16 is prevented from passing into the outlet chamber 14. However, in the first position of the stem, the outlet chamber is open to the exhaust chamber 18 and the air delivered to the outlet chamber of the valve from a connected fluid power device flows therethrough to atmosphere.
When the stem 20 is moved upward from the position shown in FIG. 1, second enlargement 30 abuts second seat 34. As a result, air is prevented from flowing to the exhaust chamber. In the second position, first enlargement 28 is moved away from first seat 32 and the compressed air delivered to the inlet chamber of the valve passes through the outlet chamber to the connected device. By moving the spool between the first and second positions, fluid may be selectively delivered to or vented from the connected device.
To prevent the escape of fluid from inside the valve around the moveable stem 20, a first seal 36 and a second seal 38 are used. First seal 36 is generally "v" shaped in cross section. It has a heel portion 40 which abuts a supporting surface 42. The supporting surface extends radially outward from the stem. Seal 36 has a first lip portion 44 that extends outward from the heel portion 40. First lip portion 44 contacts a stationary wall 46 inside the body of the valve. First seal 36 also has a second lip portion 48 which extends from the heel portion and contacts a wall 50 of the stem.
As shown in FIG. 1, the open portion of the "v" shaped first seal 36 is directed toward the interior of the valve. As a result, fluid pressure in the valve forces the lip portions against the adjacent surfaces. This enhances sealing action.
Fluid pressure from the interior of the valve may leak past second lip portion 48 into an area 52. Area 52 is bounded by the stem wall 50, the supporting surface 42, the heel portion 40 and the second lip portion 48 of the seal. The fluid pressure which enters area 52 is trapped therein. As a result, the fluid pressure tends to push the heel of seal 36 radially outward in the direction of arrow A in FIG. 1. When the heel portion 40 of the seal is deformed outward, more of lip portion 44 is pushed into contact with the wall, increasing friction and resisting movement of the stem by the solenoid or other movement means.
A similar phenomenon occurs at second seal 38. Seal 38 has a heel portion 54 which abuts a supporting surface 55 of the body. A first lip portion 56 extends from heel portion to a moveable wall 58 on the lower stem. A second lip portion 60 extends from heel portion 54 to a stationary wall 62 inside the body. Fluid pressure may leak past the second lip portion 60 into an area 64. Area 64 is bounded by the stationary wall 62, the second lip portion 60, the supporting surface 55 and the heel portion 54. When fluid pressure is trapped in area 64, the heel portion of seal 38 moves in the direction of arrow B. As a result, first lip portion 56 is pushed towards wall 58 of the stem as the seal is deformed. The combined effects of additional contact area, as well as lateral pressure, resist movement of the stem.
The combined effects of fluid leakage into areas 52 and 64 significantly increase the force that a solenoid or other movement means must supply to move the stem between the first and second positions of the valve. In addition, the added force can cause premature wearing of the seals in the areas of the valve in contact with them. This phenomenon afflicts not only pneumatic valves, but other types of fluid valves as well. Thus, there exists a need for a seal and a method that reduces the amount of force that is required to move the stem of a valve and that reduces premature wearing of the seals.